1. Field of the Invention
This invention relates to a process for producing 2-mercaptoethylamine hydrohalides. More specifically, it pertains to a process for producing 2-mercaptoethylamine hydrohalides which comprises reacting 2-mercaptothiazolines with 2-halogenoethylamine hydrohalides in the presence of water.
2. Description of the Prior Art
The 2-mercaptoethylamine hydrohalides are very useful compounds as various materials for producing medicines, intermediates for production of hair-dressing cosmetics and also as radiation protecting substances.
Among known processes for production of 2-mercaptoethylamine hydrohalides are:
(A) A process which comprises the action of an alkylenimine on a large excess of an alcohol solution of hydrogen sulfide under cooling [Ann., 566, 210 (1950); J. Chem. Soc., 1944, 5).
(B) A process which comprises reacting an alkylenimine with a dialkyl ketone, and thereafter treating the reaction product with hydrogen sulfide and then with a hydrohalic acid [Bull. Soc. Chim. Fr., 1964, 2493; Ann. 566, 210 (1950); Japanese Patent Publication No. 29444/1975; and Japanese Patent Publication No. 41569/1979].
(C) A process which comprises reacting oxazoline with hydrogen sulfide and hydrolyzing the product in an aqueous solution of hydrochloric acid (Japanese Laid-Open Patent Publication No. 128509/1979; U.S. Pat. No. 4,086,274).
(D) A process which comprises reacting an aminoalkyl sulfuric acid ester with hydrogen sulfide and an alkali polysulfide prepared from an alkali hydrosulfide and sulfur, and thereafter treating the product with hydrochloric acid (Japanese Laid-Open Patent Publication No. 11506/1980).
(E) A process which comprises hydrolyzing 2-mercaptothiazoline using hydrochloric acid or hydrobromic acid [J. Org. Chem., 25, 869 (1960); Ber., 31, 2832 (1898)].
These processes, however, have the following problems when they are used industrially.
Processes (A) to (C) require the use of alkylenimines which are carcinogenic, or poisonous hydrogen sulfide gas as starting materials. Process (D) is better than processes (A) to (C) in that it does not involve handling of hydrogen sulfide gas itself but allows it to be generated in the reaction solution. However, since the reaction is carried out under alkaline conditions, bis(2-aminoethyl)sulfides and bis(2-aminoethyl)disulfides (oxidized dimers of 2-mercaptoethylamines; trivially called cystamines), which are difficult to separate from 2-mercaptoethylamines, are formed as by-products to reduce the purity and yield of the desired 2-mercaptoethylamines. According to process (E), poisonous hydrogen sulfide gas is formed as a by-product in an amount equivalent to the amount of the starting material reacted.
It is an object of this invention to provide a process for producing highly pure 2-mercaptoethylamine hydrohalides more safely and at lower costs.